Rannoch

Rannoch was once the homeworld of the Quarians, before being overpowered by the Geth, causing the Quarians to evacuate. The Quarians now call the Migrant Fleet home. Shepard will visit there in Mass Effect 3 in order to aid the Quarians in reclaiming their lost homeworld. The planet's flora and fauna are very advanced and there are no insects on Rannoch and so the loss of potential vectors of infection played a huge role in the Quarians weak immunity system since they have had little contact with diseases on their home planet.

Legion states that the Geth don't live on the world and instead live in space stations orbiting the planet while caretaking the planet and treating it like a war memorial to remember the casualties on both sides from the Geth War.